Isocyanurates are prepared by cyclic trimerization of isocyanates. These products have excellent thermal stability and superior flame resistance and are, therefore, desirable structural units for thermally resistant plastic materials. One of the advantages of the isocyanurates is that they retain their strengths to temperatures of 160.degree.C. or more and are resistant to most organic solvents, acids, alkali, ultraviolet light and humidity. The isocyanurates can be employed as solvent-free systems, and the curing conditions can be varied over a wide range of times and temperature from rapid cure at room temperature to curing at elevated temperatures up to about 160.degree.C. while maintaining satisfactory pot life. The isocyanurates can be modified with other polymers such as polyether polyols, epoxy resins, acrylic resins and alkyd resins or they can be extended with fillers, pigments and the like.
Heretofore, a variety of catalysts has been used to promote trimerization, including quaternary hydroxides of nitrogen, phosphorus, arsenic and antimony (British Patent No. 837,120); tertiary amines, alkali or alkaline earth metal salts of 1-3 carbon carboxylic acids, alkali metal alkoxides and organic tertiary phosphines (U.S. Pat. No. 3,211,703); special tertiary amines such as N,N',N"-tris(dimethylaminopropyl) hexahydrotriazine (U.S. Pat. No. 2,993,870), and 2,4,6-tris(dimethylaminomethyl) phenol (U.S. Pat. No. 3,222,303); certain epoxide-tertiary amine mixtures (U.S. Pat. No. 2,979,485); and heavy metal compounds, such as iron acetylacetonate, which are soluble in organic solvents (U.S. Pat. No. 3,135,111).
SOME OF THESE CATALYSTS ARE RELATIVELY INACTIVE AT ROOM TEMPERATURE, AND HEAT AND/OR EXCESSIVELY HIGH LEVELS OF CATALYST ARE REQUIRED. Others are such strong bases that their presence in the final product has a detrimental effect upon the aging properties of said product, especially in the presence of chemical groups that are sensitive to nucleophilic attack. Therefore, there is still a need for new catalysts for cyclic trimerization of isocyanates which do not have these inherent disadvantages.